1. Field of the Invention
The present invention relates to a line filter assembly for use in an electrical power supply circuit in an electronic appliance for avoiding an invasion and/or a leakage of noise.
2. Description of the Prior Art
A line filter assembly is known to be used to predominantly prevent a common-mode noise component which tends to be generated between a pair of lines and the ground in an electrical power supply circuit. The line filter assemblies hitherto used are generally so constructed as shown in FIG. 1 which illustrates an electrical equivalent circuit. As shown in FIG. 1, the line filter assembly comprises a magnetic core assembly 1 forming a closed magnetic circuit in which magnetic fluxes are produced by a line current. In order to avoid a magnetic saturation of the core assembly 1, coils 2 and 3 are wound on opposite portions of the core assembly 1 so that the magnetic fluxes produced by the line current can counteract each other.
More specifically, one specific type of prior art line filter assembly is shown in FIG. 2. The illustrated line filter assembly comprises an open-ended bobbin 4 made of synthetic resin and having first and second coils 2 and 3 wound therearound, and a core assembly 1 including a pair of generally U-shaped core members each made of, for example, ferrite, and having a pair of arms opposite to each other and connected together by means of a bridge. The bobbin 4 with the coils 2 and 3 thereon is mounted on the core assembly with the respective arms of the core members inserted into the hollow of the bobbin 4 while the free ends of the arms of the core members are held in abutment with each other. After the mounting of the bobbin on the core assembly in the manner described above, a metal clamp 5 prepared from a strip of stainless steel is disposed to embrace the core members together so as thereby to complete the line filter assembly.
In a different type of the prior art line filter assembly shown in FIG. 3, the core assembly 1 is of a generally -shaped configuration made of, for example, ferrite and having an intermediate arm traversing the perimeter of the core assembly 1. Bobbin halves, which form a bobbin 6 when assembled together, are mounted on the intermediate arm from opposite directions to complete the bobbin 6 onto which the first and second coils 2 and 3 are subsequently formed by rotating the bobbin 6 about the intermediate arm in the core assembly 1 so as to thereby complete the line filter assembly.
In any one of the illustrated prior art line filter assemblies, since the two coils 2 and 3 are formed on one arm of the core assembly 1 forming the closed magnetic circuit, a space allocated for each coil is so small that the cross-sectional surface area of the coil assembly 1 must be increased or the use of the arm of increased length is necessitated for the line filter assembly to provide a high inductance. Thus, the prior art line filter assemblies have a problem associated with a space factor and, therefore, cannot be manufactured in a reduced size.
While the prior art line filter assembly shown in FIG. 3 is effective to give a high inductance because of the core assembly being of a structure forming the completely closed magnetic circuit, the intermediate arm employed in the generally -shaped core assembly 1 cannot be formed so as to have a round cross-section because of the complicated shape thereof and a space is required between the bobbin 6 and the intermediate arm so that the bobbin 6 can rotate thereabout during the winding of wires to form the coils 2 and 3. The presence of the space between the bobbin 6 and the intermediate arm of the core assembly 1 tends to hamper a manufacture of the line filter assembly in a compact size and having a reduced height